Calibration device for work machine and calibration method of working equipment parameter for work machine

ABSTRACT

A calibration device for a work machine includes: a working equipment parameter acquiring unit acquiring working equipment parameters of members of first and second actuation units; a measurement value acquiring unit acquiring respective measurement values of the work machine body and first and second actuation units measured by an external measurement device; a first calibration unit calibrating the parameter related to the member of the first actuation unit acquired by the acquiring unit based on the measurement value of the first actuation unit acquired by the acquiring unit; and a second calibration unit calibrating the working equipment parameter of the member of the second actuation unit based on the working equipment parameter of the first actuation unit calibrated by the first calibration unit and the respective measurement values of the reference points of the work machine body and first and second actuation units acquired by the acquiring unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No.PCT/JP2015/059789 filed on Mar. 27, 2015, the content of whichapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a calibration device for a work machineand a calibration method of a working equipment parameter for a workmachine.

BACKGROUND ART

A hydraulic excavator including a position detecting unit configured todetect the current position of a work point of working equipment hasbeen known. For instance, in a hydraulic excavator disclosed in PatentLiterature 1, the position coordinates of a blade edge of a bucket iscalculated based on position information from a GPS antenna.Specifically, the position coordinates of the blade edge of the bucketare calculated based on parameters such as a positional relationshipbetween the GPS antenna and a boom pin, the respective lengths of theboom, arm and bucket, and the respective direction angles of the boom,arm and bucket. The position coordinate of each of the arm and bucket iscalculated based on a sensor output value acquired from, for instance, astroke sensor, which is attached to a cylinder for swinging each of thearm and bucket to acquire an extension/retraction state of the cylinder.

With such a technique, the position of the blade edge of the bucket canbe estimated by a controller of the hydraulic excavator to move theblade edge of the bucket in conformity with a designed excavatedsurface, thereby preventing the excavated surface from being excessivelyexcavated with the bucket and efficiently performing the excavationwork.

For the above technique, it is important that the controller of thehydraulic excavator should accurately detect the position of the bladeedge of the bucket. Accordingly, in the technique disclosed in PatentLiterature 1, for instance, five of the attitudes of the blade edge ofthe bucket of the working equipment are measured by an externalmeasurement device such as a total station, and the controller of thehydraulic excavator calibrates working equipment parameters necessaryfor calculation of the position of the blade edge based on the resultingmeasurement value of the blade edge of the bucket.

CITATION LIST Patent Literature(s)

Patent Literature 1: JP-A-2012-202061

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

In the technique disclosed in Patent Literature 1, all the workingequipment parameters of the boom, arm and bucket are calibrated based onthe position of the blade edge of the bucket, which results in aninevitable error between the calibrated working equipment parameters andcorresponding true values. Further, when the blade edge is in anattitude other than the attitudes for calibration, an estimationaccuracy of the position of the blade edge of the bucket is poor ascompared with an actual measurement value of the position of the bladeedge of the bucket. It is thus difficult to reduce the error to fallwithin a predetermined acceptable range.

An object of the invention is to provide a calibration device for a workmachine and a calibration method of a working equipment parameter forthe work machine, the work machine including: a work machine body; andworking equipment including a first actuation unit swingably connectedto the work machine body and a second actuation unit swingably connectedto the first actuation unit, the calibration device and calibrationmethod being capable of highly accurate estimation of a position of areference point of the second actuation unit.

Means for Solving the Problem(s)

According to a first aspect of the invention, a calibration device for awork machine, the work machine including: a work machine body; workingequipment swingably connected to the work machine body, the workingequipment including: a first actuation unit swingably connected to thework machine body, the first actuation unit being configured to beactuated by a first hydraulic cylinder provided to the work machinebody; and a second actuation unit swingably connected to the firstactuation unit, the second actuation unit being configured to beactuated by a second hydraulic cylinder provided to the first actuationunit; first swing angle detector configured to detect swing angleinformation of the first actuation unit relative to the work machinebody; a second swing angle detector configured to detect swing angleinformation of the second actuation unit relative to the first actuationunit; an attitude calculating unit configured to calculate respectiveattitudes of the first actuation unit and the second actuation unitbased on the detected swing angle information of the first actuationunit and the second actuation unit; and an estimated positioncalculating unit configured to calculate an estimated position of areference point of the first actuation unit based on a working equipmentparameter related to a member of the first actuation unit and theattitude of the first actuation unit calculated by the attitudecalculating unit and calculate an estimated position of a referencepoint of the second actuation unit based on a working equipmentparameter related to a member of the second actuation unit and theattitude of the second actuation unit calculated by the attitudecalculating unit, the calibration device being provided to the workmachine to calibrate the working equipment parameters, the calibrationdevice includes: a measurement value acquiring unit configured toacquire a measurement value of a reference point of the work machinebody, a measurement value of the reference point of the first actuationunit and a measurement value of the reference point of the secondactuation unit, the measurement values being measured using an externalmeasurement device; a working equipment parameter acquiring unitconfigured to acquire the working equipment parameter related to themember of the first actuation unit and the working equipment parameterrelated to the member of the second actuation unit, the workingequipment parameters being used by the estimated position calculatingunit; a first calibration unit configured to calibrate the workingequipment parameter related to the member of the first actuation unitbased on the respective measurement values of the reference points ofthe work machine body and the first actuation unit measured by themeasurement value acquiring unit; and a second calibration unitconfigured to calibrate the working equipment parameter related to themember of the second actuation unit based on the working equipmentparameter related to the member of the first actuation unit calibratedby the first calibration unit and the respective measurement values ofthe reference points of the work machine body, the first actuation unitand the second actuation unit acquired by the measurement valueacquiring unit.

In the first aspect of the invention, the first calibration unitcalibrates a working equipment parameter of the member of the firstactuation unit in advance, so that second calibration unit can calibratea working equipment parameter of the member of the second actuation unitbased on the calibrated working equipment parameter and a measurementvalue of a reference point of the second actuation unit. Therefore,since an error in the working equipment parameter of the member of thefirst actuation unit is reduced, the working equipment parameter of themember of the second auction unit can be highly accurately calibrated.

According to a second aspect of the invention, in the first aspect, thefirst swing angle detector and the second swing angle detector arerespectively provided to the first hydraulic cylinder and the secondhydraulic cylinder, and each include a stroke displacement detector thatdetects a stroke displacement of the first hydraulic cylinder or thesecond hydraulic cylinder.

According to a third aspect of the invention, in the second aspect, thework machine further includes an encoder configured to detect a swingangle of the first actuation unit relative to the work machine body, andthe attitude calculating unit calibrates a reference position of thestroke displacement detector based on a reference position of the swingangle of the first actuation unit detected by the encoder.

According to a fourth aspect of the invention, in any one of the firstto third aspects, the first calibration unit calibrates the workingequipment parameter related to the member of the first actuation unit byrepeating convergence calculation until a numerical analytic formulaincluding the working equipment parameter related to the member of thefirst actuation unit and the measurement value of the reference point ofthe first actuation unit is converged within a predetermined acceptableerror range, the second calibration unit calibrates the workingequipment parameter related to the member of the second actuation unitby repeating convergence calculation until a numerical analytic formulaincluding the working equipment parameter related to the member of thesecond actuation unit and the measurement value of the reference pointof the second actuation unit is converged within a predeterminedacceptable error range, and the acceptable error range for the secondcalibration unit is larger than the acceptable error range for the firstcalibration unit.

According to a fifth aspect of the invention, in any one of the first tofourth aspects, the first actuation unit includes: a boom swingablyconnected to the work machine body with a pin to be actuated by a boomcylinder provided to the work machine body; and an arm swingablyconnected to a distal end of the boom with a pin to be actuated by anarm cylinder provided to the boom, the second actuation unit includes abucket connected to a distal end of the arm with a pin, the referencepoint of the first actuation unit is defined by the pin at the distalend of the arm, and the reference point of the second actuation unit isdefined by a distal end of the bucket in a work direction.

According to a sixth aspect of the invention, in the fifth aspect, thefirst calibration unit calibrates the working equipment parameterrelated to the member of the first actuation unit based on threeattitudes of the work machine, and the second calibration unitcalibrates the working equipment parameter related to the member of thesecond actuation unit based on two attitudes of the work machine.

According to a seventh aspect of the invention, a calibration device fora work machine, the work machine including: a work machine body; workingequipment swingably connected to the work machine body, the workingequipment including: a boom swingably connected to the work machinebody, the boom being configured to be actuated by a boom cylinderprovided to the work machine body; an arm swingably connected to theboom, the arm being configured to be actuated by an arm cylinderprovided to the boom; and a bucket swingably connected to the arm, thebucket being configured to be actuated by a bucket cylinder provided tothe arm, a boom swing angle detector configured to detect swing angleinformation of the boom relative to the work machine body; an arm swingangle detector configured to detect swing angle information of the armrelative to the boom; a bucket swing angle detector configured to detectswing angle information of the bucket relative to the arm; an attitudecalculating unit configured to calculate attitudes of the boom, the armand the bucket respectively based on the detected swing angleinformation detected by the boom swing angle detector, the arm swingangle detector and the bucket swing angle detector; and an estimatedposition calculating unit configured to calculate an estimated positionof a blade edge of the bucket based on a working equipment parameterrelated to the boom, a working equipment parameter related to the arm, aworking equipment parameter related to the bucket and the respectiveattitudes of the boom, the arm and the bucket calculated by the attitudecalculating unit, the calibration device being provided to the workmachine to calibrate the working equipment parameters, the calibrationdevice includes: a measurement value acquiring unit configured toacquire a measurement value of a reference point of the work machinebody, a measurement value of a reference point of the boom, ameasurement value of a reference point of the arm and a measurementvalue of a reference point of the bucket, the measurement values beingmeasured by an external measurement device; a working equipmentparameter acquiring unit configured to acquire the working equipmentparameters related to the boom, the arm and the bucket, the workingequipment parameters being used by the estimated position calculatingunit; a first calibration unit configured to calibrate the workingequipment parameters related to the boom and the arm based on therespective measurement values of the reference points of the workmachine body, the boom and the arm acquired by the measurement valueacquiring unit; and a second calibration unit configured to calibratethe working equipment parameter related to the bucket based on theworking equipment parameters related to the boom and the arm calibratedby the first calibration unit and the respective measurement values ofthe reference points of the work machine body, the boom, the arm and thebucket acquired by the measurement value acquiring unit.

According to an eighth aspect of the invention, a calibration method fora work machine, the work machine including: a work machine body; workingequipment swingably connected to the work machine body, the workingequipment including: a first actuation unit swingably connected to thework machine body, the first actuation unit being configured to beactuated by a first hydraulic cylinder provided to the work machinebody; and a second actuation unit swingably connected to the firstactuation unit, the second actuation unit being configured to beactuated by a second hydraulic cylinder provided to the first actuationunit; a first swing angle detector configured to detect swing angleinformation of the first actuation unit relative to the work machinebody; a second swing angle detector configured to detect swing angleinformation of the second actuation unit relative to the first actuationunit; an attitude calculating unit configured to calculate respectiveattitudes of the first actuation unit and the second actuation unitbased on the detected swing angle information of the first actuationunit and the second actuation unit; and an estimated positioncalculating unit configured to calculate an estimated position of areference point of the first actuation unit based on a working equipmentparameter related to a member of the first actuation unit and theattitude of the first actuation unit calculated by the attitudecalculating unit and calculate an estimated position of a referencepoint of the second actuation unit based on a working equipmentparameter related to a member of the second actuation unit and theattitude of the second actuation unit calculated by the attitudecalculating unit, the calibration method being performed in the workmachine to calibrate the working equipment parameters, the calibrationmethod includes: acquiring the working equipment parameter related tothe member related to the first actuation unit and the working equipmentparameter related to the member related to the second actuation unit;acquiring a measurement value of a reference point of the work machinebody, a measurement value of the reference point of the first actuationunit and a measurement value of the reference point of the secondactuation unit, the measurement values being measured by an externalmeasurement device; calibrating the working equipment parameter relatedto the member of the first actuation unit based on the measurement valueof the reference point of the work machine body and the measurementvalue of the reference point of the first actuation unit; andcalibrating the working equipment parameter related to the member of thesecond actuation unit based on the calibrated working equipmentparameter related to the member of the first actuation unit and therespective measurement values of the reference points of the workmachine body, the first actuation unit and the second actuation unit.

BRIEF DESCRIPTION OF DRAWING(S)

FIG. 1 is a perspective view showing a work machine according to anexemplary embodiment of the invention.

FIG. 2A is a schematic side view showing the work machine according tothe exemplary embodiment.

FIG. 2B is a schematic rear view showing the work machine according tothe exemplary embodiment.

FIG. 2C is a schematic plan view showing the work machine according tothe exemplary embodiment.

FIG. 3 is a control block diagram showing the work machine according tothe exemplary embodiment.

FIG. 4 is a side view showing an attached position of a first encoderaccording to the exemplary embodiment.

FIG. 5 is a perspective view showing an arrangement of the first encoderaccording to the exemplary embodiment.

FIG. 6 is a schematic view showing an arrangement of a magnetic forcesensor according to the exemplary embodiment.

FIG. 7 is a side view showing a boom of the work machine according tothe exemplary embodiment.

FIG. 8 is a side view showing an arm of the work machine according tothe exemplary embodiment.

FIG. 9 is a side view showing the arm and bucket of the work machineaccording to the exemplary embodiment.

FIG. 10 is a side view showing the bucket of the work machine accordingto the exemplary embodiment.

FIG. 11 is a side view showing a cylinder of the work machine accordingto the exemplary embodiment.

FIG. 12 is a functional block diagram showing a calibration device inthe work machine according to the exemplary embodiment.

FIG. 13 is a flow chart showing a measurement process of the workmachine, which is performed by an external measurement device, accordingto the exemplary embodiment.

FIG. 14 is a schematic view for explaining a measurement method of aposition of a boom pin of the work machine according to the exemplaryembodiment.

FIG. 15 is a schematic view for explaining a measurement method of aposition of a bucket pin of the work machine according to the exemplaryembodiment.

FIG. 16 is a schematic view for explaining a measurement method of aposition of a blade edge of the bucket of the work machine according tothe exemplary embodiment.

FIG. 17 is a flow chart for explaining effects of the exemplaryembodiment.

FIG. 18 is a schematic view for explaining the effects of the exemplaryembodiment.

DESCRIPTION OF EMBODIMENT(S)

Description will be made below on a calibration device and a calibrationmethod for a hydraulic excavator according to an exemplary embodiment ofthe invention with reference to the attached drawings.

1. Overall Arrangement of Hydraulic Excavator 1

FIG. 1 is a perspective view showing a hydraulic excavator 1, in whichthe calibration device according to the exemplary embodiment performscalibration. The hydraulic excavator 1 includes a work machine body 2and working equipment 3.

The work machine body 2 includes an undercarriage 4 and an upperstructure 5 rotatably mounted on the undercarriage 4.

In the upper structure 5, components such as a hydraulic pump 54 and anengine 54A (both described later) are housed.

A front portion of the upper structure 5 is provided with a cab 6, inwhich a display input device 71 and an operation device 51 (bothdescribed later) are provided in addition to a seat for an operator tobe seated.

The undercarriage 4 includes a pair of travel devices 4A, each of whichincludes a crawler belt 4B. The rotation of the crawler belt 4B causesthe hydraulic excavator 1 to travel. It should be noted that directionsof front, rear, right and left are defined with reference to the line ofsight of an operator seated on the seat according to the exemplaryembodiment.

The working equipment 3, which is provided to a front portion of thework machine body 2, includes a boom 31, an arm 32, a bucket 33, a boomcylinder 34, an arm cylinder 35 and a bucket cylinder 36. It should benoted that a portion including the boom 31 and the arm 32 defines afirst actuation unit according to the invention, and a portion includingthe bucket 33, a first link member 40 (described later) and a secondlink member 41 (described later) defines a second actuation unit.

The boom 31 has a base end rotatably attached to the front portion ofthe work machine body 2 with a boom pin 37. The boom pin 37 is arotation center of the boom 31 relative to the upper structure 5.

The arm 32 has a base end rotatably attached to a distal end of the boom31 with an arm pin 38. The arm pin 38 is a rotation center of the arm 32relative to the boom 31.

The bucket 33 is swingably attached to a distal end of the arm 32 with abucket pin 39. The bucket pin 39 provided to the distal end of the arm32 defines a reference point of the first actuation unit according tothe invention and also a rotation center of the bucket 33 relative tothe arm 32. The reference point of the first actuation unit mayalternatively be any position in the boom 31 or the arm 32.

The boom cylinder 34, the arm cylinder 35 and the bucket cylinder 36 arehydraulic cylinders hydraulically actuated to extend and retract. Itshould be noted that the boom cylinder 34 or the arm cylinder 35 definesa first hydraulic cylinder according to the invention, and the bucketcylinder 36 defines a second hydraulic cylinder according to theinvention.

The boom cylinder 34 has a base end rotatably attached to the upperstructure 5 with a boom cylinder foot pin 34A.

The boom cylinder 34 has a distal end rotatably attached to the boom 31with a boom cylinder top pin 34B. The boom cylinder 34 is hydraulicallyextended/retracted to move the boom 31.

The arm cylinder 35 has a base end rotatably attached to the boom 31with an arm cylinder foot pin 35A.

The arm cylinder 35 has a distal end rotatably attached to the arm 32with an arm cylinder top pin 35B. The arm cylinder 35 is hydraulicallyextended/retracted to move the arm 32.

The bucket cylinder 36 has a base end rotatably attached to the arm 32with a bucket cylinder foot pin 36A.

The bucket cylinder 36 has a distal end rotatably attached to a firstend of the first link member 40 and a first end of the second linkmember 41 with a bucket cylinder top pin 36B.

A second end of the first link member 40 is rotatably attached to thedistal end of the arm 32 with a first link pin 40A.

A second end of the second link member 41 is rotatably attached to thebucket 33 with a second link pin 41A. The bucket cylinder 36 ishydraulically extended/retracted to move the bucket 33.

FIGS. 2A to 2C schematically show an arrangement of the hydraulicexcavator 1. FIG. 2A is a side view showing the hydraulic excavator 1.FIG. 2B is a rear view showing the hydraulic excavator 1. FIG. 2C is aplan view showing the hydraulic excavator 1. As shown in FIG. 2A, L1denotes a length of the boom 31 defined between the boom pin 37 and thearm pin 38. L2 denotes a length of the arm 32 defined between the armpin 38 and the bucket pin 39. L3 denotes a length of the bucket 33defined between the bucket pin 39 and a blade edge P of the bucket 33.It should be noted that the blade edge P of the bucket 33 defines areference point of the second actuation unit according to the invention.The reference point of the second actuation unit may alternatively beany position in the bucket 33.

The boom cylinder 34, the arm cylinder 35 and the bucket cylinder 36 arerespectively provided with a boom cylinder stroke sensor 42, an armcylinder stroke sensor 43 and a bucket cylinder stroke sensor 44 (swingangle detectors).

The cylinder stroke sensors 42 to 44 are respectively provided atlateral sides of the hydraulic cylinders 34 to 36 to detect cylinderstrokes. Based on the detected respective stroke lengths of thehydraulic cylinders 34 to 36 (i.e., swing angle information), anattitude calculating unit 72C of a display controller 72 is configuredto calculate a swing angle of the boom 31 relative to the work machinebody 2, a swing angle of the arm 32 relative to the boom 31, and a swingangle of the bucket 33 relative to the arm 32. It should be noted thatthe swing angle information may alternatively be detected by anglesensors individually attached to swingable portions of the workingequipment in place of the swing angle detectors.

Specifically, based on the stroke length of the boom cylinder 34detected by the boom cylinder stroke sensor 42, the attitude calculatingunit 72C of the display controller 72 (described later) calculates aswing angle α of the boom 31 relative to a z-axis of a vehicle bodycoordinate system (described later) as shown in FIG. 2A.

Based on the stroke length of the arm cylinder 35 detected by the armcylinder stroke sensor 43, the attitude calculating unit 72C of thedisplay controller 72 calculates a swing angle β of the arm 32 relativeto the boom 31.

Based on the stroke length of the bucket cylinder 36 detected by thebucket cylinder stroke sensor 44, the attitude calculating unit 72C ofthe display controller 72 calculates a swing angle γ of the bucket 33relative to the arm 32. A method for calculating the swing angles α, β,γ will be described later.

A first encoder 42A is provided at a position of the boom pin 37, and asecond encoder 43A is provided at a position of the arm pin 38.

The first encoder 42A, which defines a reference position at apredetermined angle position within a swingable range of the boom 31,outputs a pulse signal to the attitude calculating unit 72C of thedisplay controller 72.

The second encoder 43A, which defines a reference position at apredetermined angle position within a swingable range of the arm 32,outputs a pulse signal to the attitude calculating unit 72C of thedisplay controller 72.

The attitude calculating unit 72C calibrates a reference position of theboom cylinder stroke sensor 42 based on the pulse signal outputted fromthe first encoder 42A, and calibrates the arm cylinder stroke sensor 43based on the pulse signal outputted from the second encoder 43A.

The first encoder 42A and the second encoder 43A respectively definereset sensors for the boom cylinder stroke sensor 42 and the armcylinder stroke sensor 43.

With the above arrangement, stroke positions obtained from detectionresults of the cylinder stroke sensors 42, 43 can each be reset to thereference position to reduce an error, which results in highly accurateestimation of the position of the bucket pin 39 at the distal end of thearm 32.

Specifically, as shown in FIG. 4, the boom cylinder stroke sensor 42 isprovided at a distal end of a cylinder tube 341 of the boom cylinder 34to detect a stroke displacement of a piston 342. The first encoder 42Ais provided at a swingable position of the boom 31 to calibrate the boomcylinder stroke sensor 42. As shown in FIG. 5, the first encoder 42Aincludes a light emitter 42A1, a disk 42A2 and a light receiver 42A3.

The light emitter 42A1 includes a light-emitting element that emits abeam to the light receiver 42A3.

The disk 42A2, which is rotatably held, includes: a plurality of slits42A4 circumferentially arranged at a predetermined pitch; and a singleslit 42A5 provided near the center of the disk 42A2 relative to theslits 42A4. The slit 42A5 is provided at a position corresponding to thereference position within the swingable range of the boom 31 (e.g.,substantially the middle of the swingable range of the boom 31.

The light receiver 42A3 includes a plurality of light-receiving elements42A6 provided at a position corresponding to the light emitter 42A1, andoutputs the pulse signal when the light-receiving elements 42A6 receivelight.

The disk 42A2 of the first encoder 42A rotates in accordance with theswinging movement of the boom 31. When the slit 42A5 passes under thelight emitter 42A1 during the rotation of the disk 42A2, light emittedfrom the light emitter 42A1 is received by the light-receivingelement(s) 42A6 of the light receiver 42A3 through the slit 42A5. Uponreception of the light, the light-receiving element(s) 42A6 outputs thepulse signal to the attitude calculating unit 72C. It should be notedthat the second encoder 43A provided to the arm pin 38 has the samearrangement and effects as described above.

In response to input of the pulse signal, the attitude calculating unit72C reads a signal value of the boom cylinder stroke sensor 42 andcalibrates the reference position.

The bucket 33 cannot be provided with an encoder, which is intended tobe used in a waterproof environment. Accordingly, in order to detectthat the reference position is passed, the bucket cylinder 36 isprovided with a magnetic force sensor 44A to detect the passage of amagnet provided to the bucket cylinder 36.

As shown in FIG. 6, the magnetic force sensor 44A is attached to anouter surface of a cylinder tube 361 of the bucket cylinder 36. Themagnetic force sensor 44A includes two sensors 44B, 44C spaced at apredetermined distance along a linear movement direction of a piston362.

The sensors 44B, 44C are provided to known reference positions, and thepiston 362 is provided with a magnet 44D generating magnetic lines. Thesensors 44B, 44C each transmit the magnetic lines generated by themagnet 44D to detect a magnetic force (magnetic flux density), andoutput an electric signal (voltage) corresponding to the magnetic force(magnetic flux density).

The signal detected by each of the sensors 44B, 44C is outputted to thedisplay controller 72. Based on the detection results of the sensors44B, 44C, the display controller 72 resets a stroke position obtainedfrom the detection result of the bucket cylinder stroke sensor 44 to thereference position.

The magnetic force sensor 44A, which magnetically detects the referenceposition, is likely to cause a variation in the stroke accuracy of thebucket 33, so that the detected stroke value of the bucket 33 may have alarge error as compared with those of the boom 31 and the arm 32, whichemploy the encoders 42A, 43A as the reset sensors.

As shown in FIG. 2A, the work machine body 2 includes a positiondetector 45 that detects the current position of the work machine body 2of the hydraulic excavator 1. The position detector 45 includes twoantennas 46, 47 for real time kinematic-global navigation satellitesystems (RTK-GNSS) shown in FIG. 1 and a position calculator 48 shown inFIG. 2A. It should be noted that the antennas 46, 47 may be provided toa handrail on the top of the upper structure 5.

The antennas 46, 47 are spaced from an origin O of the vehicle bodycoordinate system x-y-z (described later) along x-axis, y-axis andz-axis (see FIGS. 2A to 2C) respectively at predetermined distances(i.e., Lbdx, Lbdy, Lbdz).

A signal corresponding to a GNSS radio wave received by the antennas 46,47 is inputted to the position calculator 48. The position calculator 48detects the current position of each of the antennas 46, 47 in a globalcoordinate system. It should be noted that X-Y-Z denotes the globalcoordinate system, XY denotes a horizontal plane, and Z denotes avertical direction. Further, the global coordinate system, which is acoordinate system based on GNSS measurement, is defined with its originfixed on the earth.

In contrast, the vehicle body coordinate system (described later) is acoordinate system defined with its origin O fixed in the work machinebody 2 (specifically, the upper structure 5).

The antenna 46, which may be referred to as “reference antenna 46”,hereinafter), is intended for detection of the current position of thework machine body 2. The antenna 47, which may be referred to as“direction antenna 47”, hereinafter), is intended for detection of anorientation of the work machine body 2 (specifically, the upperstructure 5). Based on the respective positions of the reference antenna46 and the direction antenna 47, the position detector 45 detects adirection angle of the x-axis of the vehicle body coordinate (describedlater) in the global coordinate system. It should be noted that theantennas 46, 47 may be GPS antennas.

As shown in FIGS. 2A, 2B, 2C, the work machine body 2 includes aninertial measurement unit (IMU) 49 that measures an inclination angle ofthe vehicle body. An angular velocity and an acceleration of each of aroll angle (θ1: see FIG. 2B) in a Y-direction and a pitch angle (θ2: seeFIG. 2C) in an X-direction are outputted from the IMU 49.

FIG. 3 is a block diagram showing an arrangement of a control system ofthe hydraulic excavator 1.

The hydraulic excavator 1 includes the operation device 51, a workingequipment controller 52, a hydraulic control circuit 53, the hydraulicpump 54, a hydraulic motor 61, the engine 54A and a display system 70.

The operation device 51 includes a working equipment operation lever 55and a working equipment operation detecting unit 56.

The working equipment operation lever 55 includes right and leftoperation levers 55R, 55L. The left operation lever 55L is operatedright and left to provide a command for turning the upper structure 5right and left, and is operated back and forth to provide adumping/excavation command to the arm 32. The right operation lever 55Ris operated right and left to provide a dumping/excavation command tothe bucket 33, and is operated back and forth to provide a command forvertically moving the boom 31.

Working equipment operation detecting units 56L, 56R detect theoperation of the working equipment operation lever 55, and outputs thedetected operation in the form of a detection signal to the workingequipment controller 52. An operation command may be provided from theworking equipment operation lever 55 to the hydraulic control circuit 53in a pilot hydraulic manner or in an electrical lever manner. In theelectrical lever manner, the operation command is converted into anelectrical signal through, for instance, a potentiometer and inputted tothe working equipment controller 52. In the pilot hydraulic method, aproportional valve is actuated with a pilot hydraulic pressure generatedby a lever operation to regulate the flow rate of a hydraulic fluid.Further, a pilot pressure, which is detected by a pressure sensor, isconverted into an electrical signal and inputted to the workingequipment controller 52.

A travel operation lever 59 is operated by an operator to drive thehydraulic excavator 1. A travel operation detecting unit 60 supplies ahydraulic pressure to the hydraulic motor 61 of the undercarriage 4 inaccordance with the operation of the travel operation lever 59.

The working equipment controller 52 includes a storage 52A (e.g., RAM orROM) and an arithmetic unit 52B (e.g., CPU). The working equipmentcontroller 52 mainly controls the movement of the working equipment 3.The working equipment controller 52 generates a control signal formoving the working equipment 3 in accordance with the operation of theworking equipment operation lever 55, and outputs the control signal tothe hydraulic control circuit 53.

The hydraulic control circuit 53, which includes hydraulic controlequipment including a proportional control valve and an EPC valve,controls a flow rate of a hydraulic oil supplied to the hydrauliccylinders 34 to 36 from the hydraulic pump 54 based on the controlsignal from the working equipment controller 52.

The hydraulic cylinders 34 to 36 are actuated in accordance with thehydraulic oil supplied through the hydraulic control circuit 53 to movethe working equipment 3.

When the proportional valve is actuated by the operation of a turningoperation lever, the hydraulic motor 61 is driven to turn the upperstructure 5. It should be noted that a rotary motor for driving theupper structure 5 may be not hydraulically but electrically driven.

The hydraulic excavator 1 includes the display system 70. The displaysystem 70 is configured to provide an operator with information forexcavating the ground in a work area into a designed landform (describedlater). The display system 70 includes the display input device 71, thedisplay controller 72 and a calibration unit 80. It should be noted thatthe functions of the display system 70 may be provided in the form ofindividual controllers.

The display input device 71 includes an input unit 71A in the form of atouch panel and a display unit 71B, which may be a liquid crystaldisplay (LCD). The display input device 71 displays a guide screen forproviding the information for excavation. The guide screen may alsodisplay various keys, which are to be touched by an operator to performthe various functions of the display system 70.

The input unit 71A, which is used by an operator to input various typesof information such as a measurement value, may be a keyboard or a touchpanel.

The display controller 72 performs various functions of the displaysystem 70. The display controller 72 and the working equipmentcontroller 52 can communicate with each other through a wire orwirelessly. The display controller 72 includes a storage 72A, which maybe a known device (e.g., RAM or ROM), a position calculating unit 72B(e.g., CPU) and the attitude calculating unit 72C.

The position calculating unit 72B performs various calculations fordisplaying the guide screen based on various types of data stored in thestorage 72A and a detection result of the position detector 45.

Based on detection values of the cylinder stroke sensors 42 to 44, theattitude calculating unit 72C calculates attitude angles, i.e., theswing angle α of the boom 31, the swing angle β of the arm 32 and theswing angle γ of the bucket 33, from cylinder strokes detected by thecylinder stroke sensors 42 to 44 respectively provided to the boom 31,the arm 32 and the bucket 33. The attitude calculating unit 72C alsoallows the encoders 42A, 43A and the magnetic force sensor 44A to resetstroke values acquired by the cylinder stroke sensors 42 to 44 of thehydraulic cylinders. The attitude calculating unit 72C calculates a rollangle θ1 and a pitch angle θ2 of the hydraulic excavator 1 from theangular velocity and the acceleration obtained from the IMU 49.

Designed landform data is created in advance and stored in the storage72A of the display controller 72. The designed landform data isinformation regarding a three-dimensional designed landform and theposition thereof. The designed landform shows a target form of theground to be excavated. The display controller 72 displays the guidescreen on the display input device 71 based on the designed landformdata and data such as the detection results of the various sensors.

The storage 72A also stores a working equipment parameter.

3. Method for Calculating Position of Blade Edge P of Bucket 33

Next, the method for calculating the position of the blade edge P of thebucket 33 will be described in detail. The attitude calculating unit 72Cof the display controller 72 calculates an estimated position of theblade edge P of the bucket 33 based on the detection value of theposition detector 45 and a plurality of parameters stored in the storage72A.

The parameters include the working equipment parameter and an antennaparameter. The working equipment parameter includes a plurality ofparameters indicating the respective dimensions and swing angles of theboom 31, the arm 32 and the bucket 33. The antenna parameter includes aplurality of parameters indicating a positional relationship betweeneach of the antennas 46, 47 and the boom 31.

As shown in FIG. 3, the position calculating unit 72B of the displaycontroller 72 includes a first estimated position calculating unit 72Dand a second estimated position calculating unit 72E. The firstestimated position calculating unit 72D calculates an estimated positionof the blade edge P of the bucket 33 in the vehicle body coordinatesystem based on the working equipment parameter(s).

The second estimated position calculating unit 72E calculates anestimated position of the blade edge P of the bucket 33 in the globalcoordinate system from: the antenna parameter; the respective estimatedpositions of the antennas 46, 47 in the global coordinate systemdetected by the position detector 45; and the estimated position of theblade edge P of the bucket 33 in the vehicle body coordinate systemcalculated by the first estimated position calculating unit 72D.Specifically, the estimated position of the blade edge P of the bucket33 is calculated as follows.

First, as shown in FIG. 2, the vehicle body coordinate system x-y-z isdefined with its origin O at a rotation center of the upper structure 5.It should be noted that the x-axis of the vehicle body coordinate systemcorresponds to a front-and-rear direction of the vehicle body, they-axis corresponds to a right-and-left direction of the vehicle body,and the z-axis corresponds to a vertical direction of the vehicle body.

The boom pin 37 is defined as a reference position of the hydraulicexcavator 1 hereinbelow. The position of the boom pin 37 (i.e., aposition of a midpoint of the boom pin 37 in a vehicle-width direction)is actually defined as the coordinates of the position of the boom pin37 in the vehicle body coordinate system. The reference position of thehydraulic excavator 1 may be anywhere on the upper structure 5.

Based on the detection results of the cylinder stroke sensors 42, 43,44, the current swing angles α, β, γ of the boom 31, the arm 32 and thebucket 33 are calculated.

The coordinates (x, y, z) of the blade edge P of the bucket 33 in thevehicle body coordinate system are calculated from the swing angles α,β, γ of the boom 31, the arm 32 and the bucket 33 and lengths L1, L2, L3of the boom 31, the arm 32 and the bucket 33 (work parameters) by thefollowing equations (1).

Equations 1x=L1 sin α+L2 sin(α+β)+L3 sin(α+β+γ)y=0z=L1 cos α+L2 cos(α+β)+L3 cos(α+β+γ)  (1)

The coordinates (x, y, z) of the blade edge P of the bucket 33 in thevehicle body coordinate system calculated by the equations (1) areconverted into coordinates (X, Y, Z) in the global coordinate system bythe following equation (2).

$\begin{matrix}{\mspace{79mu}{{Equation}\mspace{14mu} 2}} & \; \\{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {{\begin{pmatrix}{\cos\;\kappa\mspace{11mu}\cos\;\varphi} & \begin{matrix}{{\cos\;\kappa\mspace{11mu}\sin\;\varphi\mspace{11mu}\sin\;\omega} +} \\{\sin\;\kappa\mspace{11mu}\cos\;\omega}\end{matrix} & {\begin{matrix}{{{{- \cos}\;\kappa\mspace{11mu}\sin\;\varphi\mspace{11mu}\cos\;\omega} +}\;} \\{\sin\;\kappa\mspace{11mu}\sin\;\omega}\end{matrix}\;} \\{{- \sin}\;\kappa\mspace{11mu}\cos\;\varphi} & \begin{matrix}{{{- \sin}\;\kappa\mspace{11mu}\sin\;\varphi\mspace{11mu}\sin\;\omega} +} \\{\cos\;\kappa\mspace{11mu}\cos\;\omega}\end{matrix} & \begin{matrix}{{\sin\;\kappa\mspace{11mu}\sin\;\varphi\mspace{11mu}\cos\;\omega} +} \\{\cos\;\kappa\mspace{11mu}\sin\;\omega}\end{matrix} \\{\sin\;\varphi} & {{- \cos}\;\varphi\mspace{11mu}\sin\;\omega} & {\cos\;\varphi\mspace{11mu}\cos\;\omega}\end{pmatrix}\begin{pmatrix}x \\y \\z\end{pmatrix}} + \begin{pmatrix}A \\\begin{matrix}B \\C\end{matrix}\end{pmatrix}}} & (2)\end{matrix}$

In the above equation, ω, φ and κ are represented by the followingequations (3).

$\begin{matrix}{{Equation}\mspace{14mu} 3} & \; \\{{\omega = {\arcsin( \frac{\sin\;{\theta 1}}{\cos\;\varphi} )}}{\varphi = {\theta 2}}{\kappa = {- {\theta 3}}}} & (3)\end{matrix}$

In the above equations, θ1 represents the roll angle as described above.θ2 represents the pitch angle. As shown in FIG. 2(C), θ3 represents theyaw angle, which corresponds to the direction angle of the x-axis of thevehicle body coordinate system in the global coordinate system. The yawangle θ3 is thus calculated based on the respective positions of thereference antenna 46 and the direction antenna 47 detected by theposition detector 45. (A, B, C) represents the coordinates of the originof the vehicle body coordinate system in the global coordinate system.

The antenna parameter indicates a positional relationship between eachof the antennas 46, 47 and the origin of the vehicle body coordinatesystem (i.e., a positional relationship between each of the antennas 46,47 and the midpoint of the boom pin 37 in the vehicle-width direction).

Specifically, as shown in FIGS. 2B and 2C, the antenna parameterincludes: a distance Lbbx between the boom pin 37 and the referenceantenna 46 in an x-axis direction in the vehicle body coordinate system;a distance Lbby between the boom pin 37 and the reference antenna 46 ina y-axis direction in the vehicle body coordinate system; and a distanceLbbz between the boom pin 37 and the reference antenna 46 in a z-axisdirection in vehicle body coordinate system. In addition, the antennaparameter includes: a distance Lbdx between the boom pin 37 and thedirection antenna 47 in the x-axis direction in the vehicle bodycoordinate system; a distance Lbdy between the boom pin 37 and thedirection antenna 47 in the y-axis direction in the vehicle bodycoordinate system; and a distance Lbdz between the boom pin 37 and thedirection antenna 47 in the z-axis direction in vehicle body coordinatesystem.

(A, B, C) is calculated based on the respective coordinates of theantennas 46, 47 in the global coordinate system detected by the antennas46, 47 and the antenna parameter.

The display controller 72 calculates a distance between thethree-dimensional designed landform and the blade edge P of the bucket33 based on the current position of the blade edge P of the bucket 33calculated as described above and the designed landform data stored inthe storage 72A. The calculated distance may be displayed on the displayunit 71B and/or may be used as a parameter for excavation control.

Next, description will be made on a method for calculating the currentswing angles α, β, γ of the boom 31, the arm 32 and the bucket 33 basedon the detection results of the cylinder stroke sensors 42, 43, 44.

FIG. 7 is a side view showing the boom 31. The swing angle α of the boom31 is represented by the following equation (4) using the workingequipment parameters shown in FIG. 7.

$\begin{matrix}{\mspace{79mu}{{Equation}\mspace{14mu} 4}} & \; \\{\alpha = {\pi - {\arctan( \frac{Lboom2\_ x}{Lboom2\_ z} )} - {\arccos( \frac{{{Lboom}\; 1^{2}} + {{Lboom}\; 2^{2}} - {boom\_ cyl}^{2}}{2*{Lboom}\; 1*{Lboom}\; 2} )} + {\arctan( \frac{Lboom1\_ z}{Lboom1\_ x} )}}} & (4)\end{matrix}$

As shown in FIG. 7, Lboom2_x (a working equipment parameter of the boom31) represents a distance between the boom cylinder foot pin 34A and theboom pin 37 in a horizontal direction of the work machine body 2 wherethe boom 31 is attached (corresponding to the x-axis direction in thevehicle body coordinate system). Lboom2_z (a working equipment parameterof the boom 31) represents a distance between the boom cylinder foot pin34A and the boom pin 37 in a vertical direction of the work machine body2 where the boom 31 is attached (corresponding to the z-axis directionin the vehicle body coordinate system). Lboom1 (a working equipmentparameter of the boom 31) represents a distance between the boomcylinder top pin 34B and the boom pin 37. Lboom2 (a working equipmentparameter of the boom 31) represents a distance between the boomcylinder foot pin 34A and the boom pin 37. boom_cyl (a working equipmentparameter of the boom 31) represents a distance between the boomcylinder foot pin 34A and the boom cylinder top pin 34B. Lboom1 (aworking equipment parameter of the boom 31) represents a distancebetween the boom cylinder top pin 34B and the boom pin 37 in azboom-axial direction. It should be noted that a direction connectingthe boom pin 37 and the arm pin 38 in a side view is defined as an xboomaxis, and a direction perpendicular to the xboom axis is defined as azboom axis. Lboom1_x (a working equipment parameter of the boom 31)represents a distance between the boom cylinder top pin 34B and the boompin 37 in an xboom-axial direction.

FIG. 8 is a side view showing the arm 32. The swing angle β of the arm32 is represented by the following equation (5) using the workingequipment parameters shown in FIGS. 7 and 8.

$\begin{matrix}{\mspace{79mu}{{Equation}{\mspace{11mu}\;}5}} & \; \\{\beta = {{\arctan( \frac{Lboom3\_ z}{Lboom3\_ x} )} + {\arccos( \frac{{{Lboom}\; 3^{2}} + {{Larm}\; 2^{2}} - {arm\_ cyl}^{2}}{2*{Lboom}\; 3*{Larm}\; 2} )} + {\arctan( \frac{Larm2\_ z}{Larm2\_ x} )} + {\arctan( \frac{Larm1\_ x}{Larm1\_ z} )} - \pi}} & (5)\end{matrix}$

As shown in FIG. 8, Lboom3_z (a working equipment parameter of the boom31) represents a distance between the arm cylinder foot pin 35A and thearm pin 38 in the zboom-axial direction. Lboom3_x (a working equipmentparameter of the boom 31) represents a distance between the arm cylinderfoot pin 35A and the arm pin 38 in the xboom-axial direction. Lboom3 (aworking equipment parameter of the boom 31) represents a distancebetween the arm cylinder foot pin 35A and the arm pin 38. As shown inFIG. 8, Larm2 (a working equipment parameter of the arm 32) represents adistance between the arm cylinder top pin 35B and the arm pin 38. Asshown in FIG. 7, arm_cyl (a working equipment parameter of the arm 32)represents a distance between the arm cylinder foot pin 35A and the armcylinder top pin 35B.

As shown in FIG. 8, Larm2_x (a working equipment parameter of the arm32) represents a distance between the arm cylinder top pin 35B and thearm pin 38 in an xarm2-axial direction. Larm2_z (a working equipmentparameter of the arm 32) represents a distance between the arm cylindertop pin 35B and the arm pin 38 in a zarm2-axial direction.

It should be noted that a direction connecting the arm cylinder top pin35B and the bucket pin 39 in a side view is defined as an xarm2 axis,and a direction perpendicular to the xarm2 axis is defined as a zarm2axis. Larm1_x (a working equipment parameter of the arm 32) represents adistance between the arm pin 38 and the bucket pin 39 in the xarm2-axialdirection. Larm1_z (a working equipment parameter of the arm 32)represents a distance between the arm pin 38 and the bucket pin 39 inthe zarm2-axial direction. Further, a direction connecting the arm pin38 and the bucket pin 39 in a side view is defined as an xarm1 axis. Theswing angle β of the arm 32 is an angle between the xboom axis and thexarm1 axis.

FIG. 9 is a side view showing the bucket 33 and the arm 32. FIG. 10 is aside view showing the bucket 33. The swing angle γ of the bucket 33 isrepresented by the following equation (6) using the working equipmentparameters shown in FIGS. 7 to 10.

$\begin{matrix}{\mspace{79mu}{{Equation}{\mspace{11mu}\;}6}} & \; \\{\gamma = {{\arctan( \frac{Larm1\_ z}{Larm1\_ x} )} + {\arctan( \frac{Larm3\_ z2}{Larm3\_ x2} )} + {\arccos( \frac{{Ltmp}^{2} + {{Larm}\; 4^{2}} - {{Lbucket}\; 1^{2}}}{2*{Ltmp}*{Larm}\; 4} )} + {\arccos( \frac{{Ltmp}^{2} + {{Lbucket}\; 3^{2}} - {{Lbucket}\; 2^{2}}}{2*{Ltmp}*{Lbucket}\; 3} )} + {\arctan( \frac{Lbucket4\_ x}{Lbucket4\_ z} )} + \frac{\pi}{2} - \pi}} & (6)\end{matrix}$

As shown in FIG. 8, Larm3_z2 (a working equipment parameter of the arm32) represents a distance between the first link pin 40A and the bucketpin 39 in the zarm2-axial direction. Larm3_x2 (a working equipmentparameter of the arm 32) represents a distance between the first linkpin 40A and the bucket pin 39 in the xarm2-axial direction.

As shown in FIG. 10, Ltmp (a working equipment parameter of the arm 32)represents a distance between the bucket cylinder top pin 36B and thebucket pin 39. Larm4 (a working equipment parameter of the arm 32)represents a distance between the first link pin 40A and the bucket pin39. Lbucket1 (a working equipment parameter of the bucket 33) representsa distance between the bucket cylinder top pin 36B and the first linkpin 40A. Lbucket3 (a working equipment parameter of the bucket 33)represents a distance between the bucket pin 39 and the second link pin41A. Lbucket2 (a working equipment parameter of the bucket 33)represents a distance between the bucket cylinder top pin 36B and thesecond link pin 41A.

As shown in FIG. 10, Lbucket4_x (a working equipment parameter of thebucket 33) represents a distance between the bucket pin 39 and thesecond link pin 41A in an xbucket-axial direction. Lbucket4_z (a workingequipment parameter of the bucket 33) represents a distance between thebucket pin 39 and the second link pin 41A in a zbucket-axial direction.

It should be noted that a direction connecting the bucket pin 39 and theblade edge P of the bucket 33 in a side view is defined as an xbucketaxis, and a direction perpendicular to the xbucket axis is defined as azbucket axis. The swing angle γ of the bucket 33 is an angle between thexbucket axis and the xarm1 axis. Ltmp described above is represented bythe following equation (7).

$\begin{matrix}{\mspace{79mu}{{Equation}\mspace{14mu} 7}} & \; \\{\mspace{79mu}{{{Ltmp} = \sqrt{{{Larm}\; 4^{2}} + {{Lbucket}\; 1^{2}} - {2{Larm}\; 4*{Lbucket}\; 1*\cos\;\phi}}}{\phi = {\pi + \sqrt{\frac{Larm3\_ z2}{Larm3\_ x2}} - \sqrt{\frac{{Larm3\_ z1} - {Larm3\_ z2}}{{Larm3\_ x1} - {Larm3\_ x2}}} - {\arccos\{ \frac{{{Lbucket}\; 1^{2}} + {{Larm}\; 3^{2}} - {bucket\_ cyl}^{2}}{2*{Lbucket}\; 1*{Larm}\; 3} \}}}}}} & (7)\end{matrix}$

As shown in FIG. 8, Larm3 (a working equipment parameter of the arm 32)represents a distance between the bucket cylinder foot pin 36A and thefirst link pin 40A. Larm3_x1 (a working equipment parameter of the arm32) represents a distance between the bucket cylinder foot pin 36A andthe bucket pin 39 in the xarm2-axial direction. Larm3_z1 (a workingequipment parameter of the arm 32) represents a distance between thebucket cylinder foot pin 36A and the bucket pin 39 in the zarm2-axialdirection.

boom_cyl described above is a value obtained by adding a boom cylinderoffset working parameter boft (a working equipment parameter of the boom31) to a stroke length bss of the boom cylinder 34 detected by the boomcylinder stroke sensor 42, as shown in FIG. 11. Similarly, arm_cyl is avalue obtained by adding an arm cylinder offset working equipmentparameter aoft (a working equipment parameter of the arm 32) to a strokelength as of the arm cylinder 35 detected by the arm cylinder strokesensor 43. Similarly, bucket_cyl is a value obtained by adding a bucketcylinder offset working equipment parameter bkoft (a working equipmentparameter of the bucket 33 including a minimum distance of the bucketcylinder 36) to a stroke length bkss of the bucket cylinder 36 detectedby the bucket cylinder stroke sensor 44.

4. Arrangement of Calibration Unit 80

The calibration unit 80 shown in FIG. 3 is a unit for calibrating theworking equipment parameter(s) necessary for calculating the swingangles α, β, γ and the position of the blade edge P of the bucket 33 inthe hydraulic excavator 1.

The calibration unit 80, which includes a calibration calculating unit83, defines a calibration device for calibrating the working equipmentparameter(s) in combination with the hydraulic excavator 1 and anexternal measurement device 84. The external measurement device 84 is adevice for measuring the position of the blade edge P of the bucket 33,and may be a total station. The calibration unit 80 is capable of datacommunication with the display controller 72 through an in-vehiclecommunication.

The calibration unit 80 includes a measurement value acquiring unit 83A(described later), which is capable of data communication with theexternal measurement device 84 through the in-vehicle communication.

The calibration calculating unit 83, which may be a CPU, calibrates theworking equipment parameter(s) based on a measurement value measured bythe external measurement device 84. The calibration of the workingequipment parameter(s) may be performed before shipment of the hydraulicexcavator 1 or at initialization after maintenance.

A calibration result of the work parameter(s) is displayed on thedisplay unit 71B of the display input device 71 to show whether thecalibration is successfully performed or another calibration needs to beperformed.

Specifically, as shown in a functional block diagram of FIG. 12, thecalibration calculating unit 83 includes the measurement value acquiringunit 83A, a coordinate system converting unit 85, a working equipmentparameter acquiring unit 86 and a parameter calibration unit 87.

The coordinate system converting unit 85 is a unit for converting themeasurement value measured by the external measurement device 84 into avalue according to the vehicle body coordinate system. Specifically,after being converted into the value according to the vehicle bodycoordinate system (the conversion into the value according to thevehicle body coordinate system will be described later in detail), themeasurement value is outputted to the parameter calibration unit 87.

The working equipment parameter acquiring unit 86 is a unit for readinga default value of the working equipment parameter(s) stored in thestorage 72A of the display controller 72, and the read value of theworking equipment parameter(s) is outputted to the parameter calibrationunit 87. It should be noted that the default value of the workingequipment parameter(s) may be selected from among the value shown in thefigure(s), a value obtained by, for instance, dimensional measurement,and a previously calibration value, as needed.

The parameter calibration unit 87 is a unit for calibrating the defaultvalue of the working equipment parameter(s) outputted from the workingequipment parameter acquiring unit 86 based on the measurement value,which has been converted into the value according to the vehicle bodycoordinate system by the coordinate system converting unit 85. Theparameter calibration unit 87 includes a first calibration unit 88 and asecond calibration unit 89.

The first calibration unit 88 is a unit for calibrating the workingequipment parameter(s) of the boom 31 and the arm 32 acquired by theworking equipment parameter acquiring unit 86.

The second calibration unit 89 is a unit for calibrating the workingequipment parameter(s) of the bucket 33 based on the working equipmentparameter(s) of the boom 31 and the arm 32 calibrated by the firstcalibration unit 88.

The calibration units 88, 89 of the parameter calibration unit 87 outputthe calibrated working equipment parameter(s) of the boom 31, the arm 32and the bucket 33 to the display unit 71B.

5. Calibration Process Performed by Calibration Unit 80

5-1. Measurement by External Measurement Device 84

FIG. 13 is a flow chart showing an operation process for calibrationthat is to be performed by a measuring person.

The measuring person first places the external measurement device 84 ata position squarely facing a lateral side of the boom pin 37 at apredetermined distance (Step S1).

The measuring person then performs measurement of the working equipmentparameter (e.g., an angle) defining a positional relationship between acontour point of the bucket 33 and a bucket connected position (thebucket pin 39) (Step S2). The dimension of the bucket 33 may be measuredusing the external measurement device 84 (working equipment dimensionmeasurement) or may alternatively be directly measured with a measure orthe like without using the external measurement device 84. In the lattercase, the measurement value may be manually inputted by an operatorusing the input unit 71A of the display input device 71.

The measuring person performs measurement of a plane of rotation usingthe external measurement device 84 (Step S3). In order to measure theplane of rotation using the total station, a position of a upperstructure is measured with a rotation angle (the yaw angle θ3) of theupper structure being changed for a plurality of times. The position ofthe upper structure may be measured by emitting an optical beam from thetotal station and detecting a reflected light from a maker such as aprism attached to, for instance, a counterweight provided to a rearportion of the work machine body 2 of the hydraulic excavator 1. Theabove measurement may be repeated at three spots on a locus of rotationto measure the plane of rotation.

The measuring person measures a lateral-side center position P1 of theboom pin 37 shown in FIG. 14 using the external measurement device 84(Step S4).

After completion of the measurement of the lateral-side center positionP1 of the boom pin 37, an operator operates the boom 31 and the arm 32to position the boom 31 and the arm 32 in a plurality of work attitudes.The measuring person measures the position of the bucket pin 39 providedto the distal end of the arm 32 in each work attitude (Step S5). Theposition of the bucket pin 39 is measured in each of three attitudes: aposition P2 where the boom 31 is fully raised; a position P3 where theboom 31 and the arm 32 are both extended in a work direction; and aposition P4 where the boom 31 is extended in the work direction with thearm 32 being retracted. It should be noted that the position of thebucket pin 39 may be measured in any attitude different from the threeattitudes.

Next, the operator operates the bucket 33 to position the bucket 33 in aplurality of bucket attitudes. The measuring person measures theposition of the blade edge P of the bucket 33 (Step S6). The position ofthe blade edge P of the bucket 33 is measured in each of two attitudeswith the blade edge P being situated at: a position P5 where the bucket33 is extended; and a position P6 where the bucket 33 is retracted. Itshould be noted that the bucket 33 may be measured in any attitudedifferent from the two attitudes.

The measuring person measures a GPS position at the end of the process(Step S7).

It should be noted that the resulting measurement values in Steps S2 toS7 are outputted to the measurement value acquiring unit 83A of thecalibration unit 80 after each measurement, and the measurement valuesinputted from the external measurement device 84 are each subjected tocoordinate conversion from the global coordinate system into the vehiclebody coordinate system by the coordinate system converting unit 85.

5-2. Calibration Process Performed by Calibration Unit 80

Next, description will be made on a parameter calibration process thatis to be performed by the calibration unit 80 with reference to a flowchart of FIG. 17.

The working equipment parameter acquiring unit 86 reads the workingequipment parameter(s) from the storage 72A of the display controller 72and outputs the working equipment parameter(s) to the parametercalibration unit 87 (Step S8).

The measurement values outputted from the external measurement device 84are each inputted to the measurement value acquiring unit 83A (Step S9).The coordinate system converting unit 85 converts each of themeasurement values inputted to the measurement value acquiring unit 83Ainto a value according to the vehicle body coordinate system (Step S10).

Each of the measurement values is converted into a value according tothe vehicle body coordinate system by a method including: determining awork plane of the working equipment 3 from the measurement positions P2to P4 of the bucket pin 39 shown in FIG. 15; determining a unit normalvector of the work plane and the coordinates of the centroid: andprojecting the measurement position P1 of the boom pin 37 shown in FIG.14 onto the work plane of the boom pin 37.

Next, the plane of rotation and a unit normal vector thereof aredetermined. The cross product of the two normal vectors of the plane ofrotation and the work plane is then taken to determine a front-and-reardirection vector of the hydraulic excavator 1.

Based on the determined front-and-rear direction vector and thedetermined work plane, a vertical direction vector (a vectorperpendicular to the front-and-rear direction and set within the workplane) is determined. Further, based on the determined front-and-reardirection vector and the determined plane of rotation, a right-and-leftdirection vector (a vector perpendicular to the front-and-rear directionand set within the plane of rotation) is determined.

Based on the front-and-rear direction, right-and-left direction andvertical direction, a rotation matrix for conversion from the coordinatesystem of the measurement values into the vehicle body coordinate systemis determined, and the measurement values are converted into positioninformation according to the vehicle body coordinate system with itsorigin fixed at the boom pin 37.

Next, the first calibration unit 88 determines the working equipmentparameter(s) of the boom 31 and the arm 32 by convergence calculationbased on the coordinates of the measurement positions P2 to P4 and thecorresponding attitudes calculated by the attitude calculating unit 72C(Step S11). Specifically, convergence calculation of a calibration valueof the working equipment parameter(s) is performed by a least squaresmethod as shown in the following equation (8).

$\begin{matrix}{\mspace{79mu}{{Equation}\mspace{14mu} 8}} & \; \\{J_{1} = {{\frac{1}{2}{\sum\limits_{k = 1}^{n}\{ {{L\; 1{\sin( {\alpha\; k} )}} + {L\; 2{\sin( {{\alpha\; k} + {\beta\; k}} )}}} \}^{2}}} + {\frac{1}{2}{\sum\limits_{k = 1}^{n}\{ {{L\; 1{\cos( {\alpha\; k} )}} + {L\; 2{\cos( {{\alpha\; k} + {\beta\; k}} )}}} \}^{2}}}}} & (8)\end{matrix}$

A value of k corresponds to the measurement positions P2 to P4 shown inFIG. 15. Therefore, n is equal to 3. (x1, z1) are the coordinates of themeasurement position P2 in the vehicle body coordinate system. (x2, z2)are the coordinates of the measurement position P3 in the vehicle bodycoordinate system. (x3, z3) are the coordinates of the measurementposition P4 in the vehicle body coordinate system. A point where thefunction J₁ of the equation (8) has a minimum value is found tocalculate the calibration value of the working equipment parameter(s).

The first calibration unit 88 determines whether or not the value of theequation (8) falls within a predetermined acceptable range (Step S12).

When an error is out of the acceptable range, the first calibration unit88 determines whether or not the convergence calculation is repeated fora predetermined number of times or less (Step S13). When the convergencecalculation is not repeated for the predetermined number (N) or more,the process returns to Step S11.

When the convergence calculation is repeated for the predeterminednumber of times (N), the first calibration unit 88 commands the displayunit 71B to display information for informing the measuring person andthe operator of a failure of the convergence calculation to inhibit theprocess from further proceeding (Step S14).

The measuring person and the operator then get back to Step S8 andrepeat the process from Step S8 to Step S11.

When determining that the error falls within the predeterminedacceptable range, the first calibration unit 88 commands the displayunit 71B to display information for informing the measuring person andthe operator of a fact that the error falls within the acceptable range(Step S14), calibrates the working equipment parameter(s) (Step S15),and permits the process to further proceed.

The first calibration unit 88 outputs the calibrated working equipmentparameter(s) of the boom 31 and the arm 32 to the second calibrationunit 89.

The second calibration unit 89 calculates a calibration value of theworking equipment parameter(s) of the bucket 33 by convergencecalculation based on the working equipment parameter(s) calibrated bythe first calibration unit 88, the measurement values of the measurementpositions in the plurality of working equipment attitudes (i.e., themeasurement positions P5, P6), and the attitudes corresponding to themeasurement positions P5, P6 calculated by the attitude calculating unit72C (Step S16). Specifically, the second calibration unit 89 calculatesthe working equipment parameter(s) by convergence calculation based onthe coordinates of the measurement position in the plurality of bucketattitudes (i.e., the measurement positions P5, P6) and the cylinderstroke lengths corresponding to the measurement positions P5, P6. Theconvergence calculation of the calibration value of the workingequipment parameter(s) is thus performed as shown in the followingequation (9).

  Equation  9$J_{2} = {{\frac{1}{2}{\sum\limits_{k = 1}^{n}\{ {{L\; 1{\sin( {\alpha\; k} )}} + {L\; 2{\sin( {{\alpha\; k} + {\beta\; k}} )}} + {L\; 3{\sin( {{\alpha\; k} + {\beta\; k} + {\gamma\; k}} )}} - {xk}} \}^{2}}} + {\frac{1}{2}{\sum\limits_{k = 1}^{n}\{ {{L\; 1{\cos( {\alpha\; k} )}} + {L\; 2{\cos( {{\alpha\; k} + {\beta\; k}} )}} + {L\; 3{\cos( {{\alpha\; k} + {\beta\; k} + {\gamma\; k}} )}} - {zk}} \}^{2}}}}$

A value of k in the equation (9) corresponds to the measurementpositions P5, P6 shown in FIG. 16. Therefore, n is equal to 2. (x4, y4)are the coordinates of the measurement position P5 in the vehicle bodycoordinate system. (x5, y5) are the coordinates of the measurementposition P6 in the vehicle body coordinate system. A point where afunction J₂ of the equation (9) has a minimum value is found tocalculate the calibration value of the working equipment parameter(s).

The second calibration unit 89 determines whether or not J₂ of theequation (9) falls within a predetermined acceptable range (Step S17).

When an error is out of the acceptable range, the second calibrationunit 89 determines whether or not the convergence calculation isrepeated for a predetermined number of times or less (Step S18). Whenthe convergence calculation is not repeated for the predetermined number(N) or more, the process returns to Step S16.

When the convergence calculation is repeated for the predeterminednumber of times (N), the first calibration unit 88 commands the displayunit 71B to display information for informing the measuring person andthe operator of a failure of the convergence calculation to inhibit theprocess from further proceeding (Step S19).

When determining that the error falls within the predeterminedacceptable range, the second calibration unit 89 commands the displayunit 71B to display information for informing the measuring person andthe operator of a fact that the error falls within the acceptable range(Step S19).

The parameter calibration unit 87 outputs the calibrated workingequipment parameter(s) to the display controller 72 so that thecalibrated working equipment parameter(s) is written as a parameter fora new working equipment file in the storage 72A of the displaycontroller 72 (Step S20).

It should be noted that an acceptable error set by the first calibrationunit 88 should be smaller than an acceptable error set by the secondcalibration unit 89 in the exemplary embodiment. This is because thatthe error in the first actuation unit (the boom 31 and the arm 32), theworking equipment dimension of which is large as compared with that ofthe bucket 33, has a larger influence on an error in the blade edge P ofthe bucket 33 than the second actuation unit (the bucket 33). Areduction in an error in the working equipment parameter(s) of the firstactuation unit thus results in a reduction in an error in the blade edgeP.

Effect(s) of Exemplary Embodiment(s)

As shown in FIG. 18, the position of the blade edge P of the bucket 33was changed within an operation range of the working equipment 3 of thehydraulic excavator 1 to check an error between the measurement value ofthe position of the blade edge P measured using the external measurementdevice 84 and the estimated value of the position of the blade edge Pcalculated based on the working equipment parameter(s).

When the calibration is performed in a typical method where the positionof the blade edge P is measured in each of five attitudes, an errorbetween an estimated position and a measurement position became large ata lower position of the bucket 33 and/or a distal end of the bucket 33in the work direction.

In contrast, according to the exemplary embodiment, the firstcalibration unit 88 can highly accurately calibrate the workingequipment parameter(s) of a member(s) of the first actuation unit basedon a cylinder stroke of the member(s) of the first actuation unit with asmall error. Further, based on the highly accurately calibrated workingequipment parameter(s) of the member(s) of the first actuation unit, theparameter(s) of a member(s) of the second actuation unit is also highlyaccurately calibrated as compared with an instance where theparameter(s) is typically calibrated. This results in a reduction in anerror between the measurement position of the blade edge P and acalculated estimated value of the position of the blade edge P.

An error is thus reduced over the whole operation range of the workingequipment 3. Especially, when the working equipment 3 has a long length,an error is considerably reduced.

Modification(s) of Exemplary Embodiment(s)

It should be understood that the scope of the invention is not limitedto the above-described exemplary embodiment(s), but includesmodifications and improvements compatible with the invention.

For instance, the hydraulic excavator 1 is subjected to calibrationaccording to the exemplary embodiment. However, the invention may beapplied to any other work machine such as a wheel loader.

The external measurement device 84 may perform the measurement processaccording to the exemplary embodiment in a different order.

The invention claimed is:
 1. A calibration device for a work machine,the work machine comprising: a work machine body; working equipmentswingably connected to the work machine body, the working equipmentcomprising: a first actuation unit swingably connected to the workmachine body, the first actuation unit being configured to be actuatedby a first hydraulic cylinder provided to the work machine body; and asecond actuation unit swingably connected to the first actuation unit,the second actuation unit being configured to be actuated by a secondhydraulic cylinder provided to the first actuation unit; a first swingangle detector configured to detect swing angle information of the firstactuation unit relative to the work machine body; a second swing angledetector configured to detect swing angle information of the secondactuation unit relative to the first actuation unit; an attitudecalculating unit configured to calculate respective attitudes of thefirst actuation unit and the second actuation unit based on the detectedswing angle information of the first actuation unit and the secondactuation unit; and an estimated position calculating unit configured tocalculate an estimated position of a reference point of the firstactuation unit based on a working equipment parameter related to amember of the first actuation unit and the attitude of the firstactuation unit calculated by the attitude calculating unit and calculatean estimated position of a reference point of the second actuation unitbased on a working equipment parameter related to a member of the secondactuation unit and the attitude of the second actuation unit calculatedby the attitude calculating unit, the calibration device being providedto the work machine to calibrate the working equipment parameters, thecalibration device comprising: a measurement value acquiring unitconfigured to acquire a measurement value of a reference point of thework machine body, a measurement value of the reference point of thefirst actuation unit and a measurement value of the reference point ofthe second actuation unit, the measurement values being measured usingan external measurement device; a working equipment parameter acquiringunit configured to acquire the working equipment parameter related tothe member of the first actuation unit and the working equipmentparameter related to the member of the second actuation unit, theworking equipment parameters being used by the estimated positioncalculating unit; a first calibration unit configured to calibrate theworking equipment parameter related to the member of the first actuationunit based on the respective measurement values of the reference pointsof the work machine body and the first actuation unit measured by themeasurement value acquiring unit; and a second calibration unitconfigured to calibrate the working equipment parameter related to themember of the second actuation unit based on the working equipmentparameter related to the member of the first actuation unit calibratedby the first calibration unit and the respective measurement values ofthe reference points of the work machine body, the first actuation unitand the second actuation unit acquired by the measurement valueacquiring unit.
 2. The calibration device for the work machine accordingto claim 1, wherein the first swing angle detector and the second swingangle detector are respectively provided to the first hydraulic cylinderand the second hydraulic cylinder, and each comprise a strokedisplacement detector that detects a stroke displacement of the firsthydraulic cylinder or the second hydraulic cylinder.
 3. The calibrationdevice for the work machine according to claim 2, wherein the workmachine further comprises an encoder configured to detect a swing angleof the first actuation unit relative to the work machine body, and theattitude calculating unit calibrates a reference position of the strokedisplacement detector based on a reference position of the swing angleof the first actuation unit detected by the encoder.
 4. The calibrationdevice for the work machine according to claim 1, wherein the firstcalibration unit calibrates the working equipment parameter related tothe member of the first actuation unit by repeating convergencecalculation until a numerical analytic formula comprising the workingequipment parameter related to the member of the first actuation unitand the measurement value of the reference point of the first actuationunit is converged within a predetermined acceptable error range, thesecond calibration unit calibrates the working equipment parameterrelated to the member of the second actuation unit by repeatingconvergence calculation until a numerical analytic formula comprisingthe working equipment parameter related to the member of the secondactuation unit and the measurement value of the reference point of thesecond actuation unit is converged within a predetermined acceptableerror range, and the acceptable error range for the second calibrationunit is larger than the acceptable error range for the first calibrationunit.
 5. The calibration device for the work machine according to claim1, wherein the first actuation unit comprises: a boom swingablyconnected to the work machine body with a pin to be actuated by a boomcylinder provided to the work machine body; and an arm swingablyconnected to a distal end of the boom with a pin to be actuated by anarm cylinder provided to the boom, the second actuation unit comprises abucket connected to a distal end of the arm with a pin, the referencepoint of the first actuation unit is defined by the pin at the distalend of the arm, and the reference point of the second actuation unit isdefined by a distal end of the bucket in a work direction.
 6. Thecalibration device for the work machine according to claim 5, whereinthe first calibration unit calibrates the working equipment parameterrelated to the member of the first actuation unit based on threeattitudes of the work machine, and the second calibration unitcalibrates the working equipment parameter related to the member of thesecond actuation unit based on two attitudes of the work machine.
 7. Acalibration device for a work machine, the work machine comprising: awork machine body; working equipment swingably connected to the workmachine body, the working equipment comprising: a boom swingablyconnected to the work machine body, the boom being configured to beactuated by a boom cylinder provided to the work machine body; an armswingably connected to the boom, the arm being configured to be actuatedby an arm cylinder provided to the boom; and a bucket swingablyconnected to the arm, the bucket being configured to be actuated by abucket cylinder provided to the arm, a boom swing angle detectorconfigured to detect swing angle information of the boom relative to thework machine body; an arm swing angle detector configured to detectswing angle information of the arm relative to the boom; a bucket swingangle detector configured to detect swing angle information of thebucket relative to the arm; an attitude calculating unit configured tocalculate attitudes of the boom, the arm and the bucket respectivelybased on the detected swing angle information detected by the boom swingangle detector, the arm swing angle detector and the bucket swing angledetector; and an estimated position calculating unit configured tocalculate an estimated position of a blade edge of the bucket based on aworking equipment parameter related to the boom, a working equipmentparameter related to the arm, a working equipment parameter related tothe bucket and the respective attitudes of the boom, the arm and thebucket calculated by the attitude calculating unit, the calibrationdevice being provided to the work machine to calibrate the workingequipment parameters, the calibration device comprising: a measurementvalue acquiring unit configured to acquire a measurement value of areference point of the work machine body, a measurement value of areference point of the boom, a measurement value of a reference point ofthe arm and a measurement value of a reference point of the bucket, themeasurement values being measured by an external measurement device; aworking equipment parameter acquiring unit configured to acquire theworking equipment parameters related to the boom, the arm and thebucket, the working equipment parameters being used by the estimatedposition calculating unit; a first calibration unit configured tocalibrate the working equipment parameters related to the boom and thearm based on the respective measurement values of the reference pointsof the work machine body, the boom and the arm acquired by themeasurement value acquiring unit; and a second calibration unitconfigured to calibrate the working equipment parameter related to thebucket based on the working equipment parameters related to the boom andthe arm calibrated by the first calibration unit and the respectivemeasurement values of the reference points of the work machine body, theboom, the arm and the bucket acquired by the measurement value acquiringunit.
 8. A calibration method for a work machine, the work machinecomprising: a work machine body; working equipment swingably connectedto the work machine body, the working equipment comprising: a firstactuation unit swingably connected to the work machine body, the firstactuation unit being configured to be actuated by a first hydrauliccylinder provided to the work machine body; and a second actuation unitswingably connected to the first actuation unit, the second actuationunit being configured to be actuated by a second hydraulic cylinderprovided to the first actuation unit; a first swing angle detectorconfigured to detect swing angle information of the first actuation unitrelative to the work machine body; a second swing angle detectorconfigured to detect swing angle information of the second actuationunit relative to the first actuation unit; an attitude calculating unitconfigured to calculate respective attitudes of the first actuation unitand the second actuation unit based on the detected swing angleinformation of the first actuation unit and the second actuation unit;and an estimated position calculating unit configured to calculate anestimated position of a reference point of the first actuation unitbased on a working equipment parameter related to a member of the firstactuation unit and the attitude of the first actuation unit calculatedby the attitude calculating unit and calculate an estimated position ofa reference point of the second actuation unit based on a workingequipment parameter related to a member of the second actuation unit andthe attitude of the second actuation unit calculated by the attitudecalculating unit, the calibration method being performed in the workmachine to calibrate the working equipment parameters, the calibrationmethod comprising: acquiring the working equipment parameter related tothe member related to the first actuation unit and the working equipmentparameter related to the member related to the second actuation unit;acquiring a measurement value of a reference point of the work machinebody, a measurement value of the reference point of the first actuationunit and a measurement value of the reference point of the secondactuation unit, the measurement values being measured by an externalmeasurement device; calibrating the working equipment parameter relatedto the member of the first actuation unit based on the measurement valueof the reference point of the work machine body and the measurementvalue of the reference point of the first actuation unit; andcalibrating the working equipment parameter related to the member of thesecond actuation unit based on the calibrated working equipmentparameter related to the member of the first actuation unit and therespective measurement values of the reference points of the workmachine body, the first actuation unit and the second actuation unit.